The invention relates to a method for braking a revolvable superstructure of a working machine, in connection with which the rotational movement of the superstructure is generated via a controllable hydrostatic transmission located in a closed hydraulic circuit, whereby the hydrostatic transmission is controlled for starting the rotational movement via a control lever that is actuated by the driver. The control lever has at least one neutral position and two switching positions for rotating the superstructure in two-directions opposing each other, whereby the braking of the superstructure is achieved by counter-steering against the given direction of rotation of the superstructure. Furthermore, the invention relates to a pivoted brake unit for braking a revolvable superstructure of a working machine comprising a revolvable superstructure which is driven by a controllable hydrostatic transmission located in a closed hydraulic circuit, whereby the hydrostatic transmission can be actuated via a control lever actuated by the driver for starting the rotational movement. Said control lever has at least one neutral position and two switching positions for rotating the superstructure in two directions of rotation opposing each other. In
In connection with working machines comprising a revolvable superstructure that is supported on a rotating bearing and comprises a rotational drive train in the form of a transmission, for example a working machine such as an excavator, a crane or the like, the revolvable superstructure is driven by a motor generating the rotational movement. Such a motor may be a hydraulic or electrical motor. In most cases, said motor effects the rotation of the superstructure of the working machine via a transmission engaging the toothing of the rotary bearing by means of a pinion.
The rotational movement of the superstructure can be slowed down in different ways.
Known are, for example friction brakes, which are located either in the revolving transmission or directly on the rotary bearing. The friction brakes are controlled in different ways. It is known to control such friction brakes by means of a pedal actuated by the driver, and to control the friction brake-automatically as soon as the motor of the rotary drive has been shifted into neutral by the operator.
Another known type of braking is braking via the motor generating the rotational movement, whereby the motor is slowed down by a constant or controllable braking valve as soon as said motor has been shifted into neutral by the driver. In connection with a drive via a hydraulic motor, a throttle, for example, located in the hydraulic circuit is connected when the control lever is in the neutral position, and the counterpressure generated via the throttle then brakes the superstructure. Similar solutions are available also for electrical drives generating the rotational movement.
Furthermore, methods or pivoted brake units of the type specified above are known as well. The superstructure is slowed down in connection with such methods and units by a counter-steering action (countering). With such a type of superstructure, the working machine is not equipped with any actual brake or braking system but fitted only with a holding brake, if necessary, which fixes the superstructure when it is at a standstill. Counter-steering is started by the driver by means of his control lever by shifting the system into the opposite direction of rotation. The motor producing the rotational movement then generates an opposite torque and brakes the superstructure. As soon as the rotational movement has come to zero, the control lever has to be shifted to neutral in order to prevent the superstructure from pivoting into the opposite direction.
Such a type of a braking system is favorable because it has a simple type of construction; however, it requires the driver to have certain skills, experience and alertness in order to safely bring the rotational movement to a standstill. Furthermore, with such a type of braking, the braking energy is recycled into the driving system and consequently leads to energy savings.
The problem of the invention is to improve the braking of the superstructure of a working machine by counter-steering in order to eliminate operational errors by the driver as far as possible and to safely bring the superstructure to a complete standstill.
Said problem is solved according to the invention with a method of the type specified above in that the rotational movement of the superstructure is automatically slowed down by counter-steering when the control lever is in a braking position, preferably in the neutral position. With the control lever in such a position, a pivoting torque set against the current rotational movement by a switching logic circuit reverses the hydrostatic pivoting pump of the hydrostatic transmission until a device monitoring the number of revolutions of the revolvable superstructure, said device being coupled to the switching logic circuit, determines that the superstructure is at a standstill.
The invention thus proposes a method by which automatic braking is accomplished by a counter-steering action that is independent of the driver, i.e. the automatic braking action takes place as soon as the driver has shifted the control lever into the braking position. Furthermore, this makes the braking process independent of the skill, experience and alertness of the driver, and braking is safely accomplished because in the course of the braking action by means of counter-steering, the rotational movement of the superstructure is constantly monitored and the braking action is stopped after the superstructure has been brought to a standstill.
In order to always start the correct counter-torque under all operating conditions of the working machine independently of the actuation of the control lever, and to bring the rotational movement to a standstill, provision is advantageously made that the given direction of rotation of the superstructure is determined by the switching logic circuit because especially if the working machine is operating in an inclined position on a gradient, it is necessary to assure that unintentional rotational movements caused by the force of down drift of the gradient will not lead to errors in the steering action. Such steering errors may occur, for example when the superstructure slightly revolves in the downhill direction while pivoting uphill before the adjusted uphill movement has become effective.
For said purpose, the rotational speed is detected via a tachometer or the like as soon as the driver has started the pivoting movement; the direction of rotation is determined by the switching logic circuit; and the automatic counter-steering action is subsequently started as soon as the driver has shifted the control lever for the pivoting movement into the braking position. The automatic counter-steering process will then remain active until the superstructure has come to a standstill. A holding brake can then be automatically triggered preferably by the switching logic circuit. The recognition of the direction of rotation is subsequently cancelled in the switching logic circuit. In this way, the switching logic circuit prevents any undesirable reversal of the direction of rotation that may be initiated if the driver rapidly counter-steers by hand.
According to the invention, the problem specified above is solved also by means of a pivoted brake unit in that a switching logic circuit is coupled with the hydrostatic pivoting pump of the hydrostatic transmission and with the control valve, and designed in such a way that it automatically brakes the rotational movement of the superstructure by counter-steering as soon as the control lever is in a braking position, preferably in the neutral position, and in that provision is made for a device monitoring the number of revolutions of the superstructure. Said device for monitoring the rotational speed is connected to the switching logic circuit in such a manner that the counter-steering action is stopped when the superstructure has come to a standstill.
The switching logic circuit of the pivoting brake unit is preferably formed by mechanical, electronic, hydraulic and/or pneumatic components, or by an electronic control unit.
Furthermore, for the reasons stated above, provision is made for a device for detecting the direction of rotation. Said device is connected to the switching logic circuit for the purpose of assuring a flawless operation of the pivoted brake unit when working machines are operating in inclined positions. Furthermore, provision is usefully made for a holding brake that is activated by the switching logic circuit when the superstructure is standing still.
Moreover, provision may be advantageously made for a pressure control valve for adjusting the counter-steering torque.
The switching logic circuit may basically comprise one (or two separate) sensors for detecting the number of revolutions and the direction of rotation of the superstructure, which permits using a simplified switching logic circuit that solves the problems arising when the working machine is operating in an inclined position as well.
The switching logic circuit may be formed also by an electronic control unit, in which the pivoting instruction as well as the number of revolutions and the direction of rotation are input by means of the controller set operated by the driver. The electronic control unit then controls the pivoted drive and the parking brake via its outputs in order to accomplish the described type of braking. Furthermore, the control unit may be suited for performing additional functions by means of a selector switch, which has to be actuated by the driver for selecting different modes of operation, i.e. different operating conditions can be set up such as, for example application of the holding brake (freewheeling), or blocking of the rotational movement by applying the holding brake and switching off the control instructions preset by the control lever actuated by the driver, or adjustment of the braking action by means of an adjustable counter-pivoting torque.